Removing Salt From Coal Mine Wastewater in a Remote, Wet Area: Full Scale Experience

Srikanth Muddasani, P.E. Veolia Water Technologies, USA

• Centralized ZLW treatment facility to handle water from six mine locations

• All six mines located within Monongahela River Basin

• Regulatory driver = Chlorides to < 218 mg/L

• Solid wastes generated are disposed in on-site landfill

• Treated effluent is discharged to creek and/or used as frac water

Project Background

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Contributing Mine Locations

18” Force Main collects water from 4 mines to the North

14” Force Main collects water from 2 mines to the South

CENTRALIZED TREATMENT FACILITY

• Centralized ZLW treatment facility is designed to treat 5 MGD (795 m3/h) of mine water

• Mine water, pretreated for metals removal where needed, conveyed from six source points to the facility through 32 miles of pipeline

• Executed through a Design-Build-Operate contract with Veolia

• June 2010 - Request for proposals issued

• April 2011 - Project awarded

• July 2011 - Construction began

• May 2013 - Full operation

The Project

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Note 1: Average Value based on the data collected between Jun 1st 2014 to Dec 31st 2014 Note 2: Average Value based on the data collected between Aug 20th,2014 to Sep 5th, 2014

Design Basis - Influent Mine Water

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Parameters Original Design Current Design1

Design Flow, gpm 3500 (795 m3/h) 2026 (460 m3/h)

pH, S.U. 5 - 10 7.39

Temperature, deg F 38 – 85 (3 – 30 deg C) 60 – 72 (15-22 deg C)

Calcium, mg/L 300 217

Magnesium, mg/L 200 104

Iron, mg/L 150 0.27

Manganese, mg/L 2 0.27

Alkalinity, mg/L CaCO3 700 - 1200 891

Sulfate, mg/L 5,500 2700 2

Chloride, mg/L 1,500 1530 2

TDS, mg/L 10,000 8600

Silica, mg/L as SiO2 10 10

Note 1: Applied to product water prior to remineralization

Effluent Water Quality Requirements

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Parameters Maximum Effluent Concentration

Chlorides, mg/L < 218

TDS, mg/L < 150 1

pH, S.U. 6 to 9

Minimum Hardness, mg/l as CaCO3 ≥ 50

• Raw Water Pretreatment System

• Reverse Osmosis System

• Thermal Brine Management System

The Process: Three Primary Components

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Process Overview

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Primary Objectives 1. Remove TDS and Chlorides 2. Zero Liquid Waste

Facility Overview

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Evaporator

Crystallizer

RO Trains

Raw Water Tank

Multimedia Filters Lime & Soda Ash Silos

Softening System

1st Stage Clarifier

Dewatering Building

• Multi-stage process

• Two aeration tanks for precipitation of metals such as manganese and iron

• Crystallization tank for removal of alkalinity and hardness

• Draft-tube reactor design

• Solids recycle

• Reduce chemical consumption

• Enhance particle growth and settling characteristics

• Conventional circular clarifier design

Chemical Softening System

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• Removes residual suspended solids in the effluent from upstream clarification and aluminum precipitation processes

• Backwash water is returned to the Raw Water Feed Tank

• Filtrate is conveyed to the RO System

Multimedia Filter System

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Reverse Osmosis System

• RO Feed Tank, followed by Cartridge Filtration

• RO Skids designed to achieve chloride and TDS specifications while operating at a high recovery rate

• Five parallel skids, each sized to handle 25% of the design flow, 1 standby

• Thirty-one pressure vessels per skid, each with seven seawater RO membrane elements

• Permeate flows to Product Water Tank, which also collects distillate from Brine Management System

• Prior to discharge, the Product Water Tank effluent is re-mineralized using carbon dioxide and lime water, to protect aquatic life

• Discharged to creek, or to a truck loading station for reuse in energy-related operations.

• Reject is sent to the thermal Brine Management System

The Process Flow - RO System

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Evaporator

• Concentric falling film unit is divided into two sections with a low concentration side and a high concentration side

• Split design to reduce overall power consumption by allowing a portion of the evaporation to occur at a lower boiling point rise than the final concentration

• Evaporator operates as a Mechanical Vapor Recompression System

• Recycle of hot vapor in the system; minimize auxiliary steam

• Distillates from the Evaporator and Crystallizer are pumped through a Feed Preheater for heat transfer to the incoming brine

• Heat exchanger for efficient energy utilization

Evaporation

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• Crystallizer includes a vapor body, recirculation pump, and forces circulation heat exchanger

• Vapors created by concentrating the slurry in the Crystallizer are recompressed and recirculated through the heater

• As the brine concentration increases, the solution becomes supersaturated and salts precipitate, resulting in a brine slurry

• A slip stream of the crystallizer slurry is sent to centrifuges for dewatering

• The result: Zero Liquid Waste

• Dewatered salt cake is disposed in the on-site landfill along with the dewatered sludge from the softening processes

Crystallization

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Thermal Brine Management System

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Crystallizer Evaporator Heat Exchanger

Distillate Tank

Crystallizer

• Dewatered Salt and Softening Sludge is brought separately to onsite landfill

• Dewatered Salt contains approximately 90 – 95% in solids concentration and Sludge contains 50 – 65% in solids concentration.

• Both passes paint filter press test

• Both Salt and Sludge are mixed before applied to landfill

• Lechate generated in landfill is collected in storage tank and metered back to thermal system

Land fill

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• Chemical Storage and Feed Systems

• Lime Water Preparation System

• RO Membrane Clean-in-Place System

• Compressed Air System

• Electrical and Control Rooms

• Laboratory

• Communications Equipment

• Maintenance and Storage Areas

• Personnel Amenities

Ancillary Support Systems

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Feed Water Conductivity

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6,000

8,000

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12,000

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16,000

18,000

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Cond

uctiv

ity (µ

s/cm

)

Days

Current Feed Conductivity Design Feed Conductivity

Original Design Conductivity = 13,000 µs/cm Current Avg Conductivity = 11,180 µs/cm

Product Water Conductivity

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Product water Cond before Remineralization = 63 µs/cm Final Effluent Discharge Cond = 142 µs/cm

0

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06/01/14 07/06/14 09/16/14 10/21/14 11/25/14 12/31/14

Cond

uctiv

ity (µ

s/cm

)

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Product Water Cond before Remin Final Eff Discharge Cond

Feed Water Chlorides

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Chlo

rides

(mg/

L)

Days

Current Feed Chlorides

Current Avg Feed Chlorides = 1,530 mg/l

Final Effluent Chlorides

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Efflu

ent C

hlor

ides

, mg/

l

Days

Final Effluent Chlorides = 16 mg/l

Please Note: Waste Estimation for design condition was estimated based on 3500 gpm flow Waste Estimation for Current Average Condition was estimated based on 2026 gpm flow

Estimated Waste Generation

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Waste Design Condition Current Average Condition

Softening Sludge (on a 100% dry basis) 6,666 lb/hr (3,030 kg/hr) 2,200 lb/hr (1,000 kg/hr)

Salt (on a 100% dry basis) 17,500 lb/hr (7,954 kg/hr) 8,710 lb/hr (3,960 kg/hr)

Total Waste Generated (on 100% dry basis) 24,166 lb/hr (10,984 kg/hr) 10,910 lb/hr (4,960 kg/hr)

• Treatment process achieves > 99% removal of chlorides using state-of-the-art membrane technology

• Energy efficient evaporation and crystallization technology for brine management

• Solid waste generated onsite is disposed into onsite landfill and leachate generated at the landfill is sent back to the facility’s thermal treatment process

• Since no liquid waste leaves the property, this facility is termed as a “zero liquid waste” (ZLW) facility

Summary

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Thank You!